Perpendicular magnetization with oxide interface

ABSTRACT

A mechanism is provided for a structure with perpendicular magnetic anisotropy. A bottom oxide layer is disposed, and a magnetic layer is disposed adjacent to the bottom oxide layer. The magnetic layer includes iron and is magnetized perpendicularly to a plane of the magnetic layer. A top oxide layer is disposed adjacent to the magnetic layer.

BACKGROUND

The present invention relates generally to magnetic memory and magneticstorage devices, and more specifically, to materials in andconfigurations for a device with perpendicular magnetization.

Spin transfer torque is an effect in which the orientation of a magneticlayer in a magnetic tunnel junction or spin valve can be modified usinga spin-polarized current. Charge carriers (such as electrons) have aproperty known as spin which is a small quantity of angular momentumintrinsic to the carrier. An electrical current is generally unpolarized(consisting of 50% spin-up and 50% spin-down electrons). A spinpolarized current is one with more electrons of either spin. By passinga current through a thick magnetic layer, one can produce aspin-polarized current. If a spin-polarized current is directed into amagnetic layer, angular momentum can be transferred to the magneticlayer, changing its magnetic orientation. This can be used to flip theorientation of the magnet.

SUMMARY

According to an exemplary embodiment, a structure with perpendicularmagnetic anisotropy is provided. The structure includes a bottom oxidelayer, and a magnetic layer adjacent to the bottom oxide layer. Themagnetic layer includes iron and is magnetized perpendicularly to aplane of the magnetic layer. A top oxide layer is adjacent to themagnetic layer.

According to another exemplary embodiment, a method of forming astructure with perpendicular magnetic anisotropy is provided. The methodincludes depositing a bottom oxide layer, and depositing a magneticlayer adjacent to the bottom oxide layer. The magnetic layer includesiron and is magnetized perpendicularly to a plane of the magnetic layer.A top oxide layer is deposited adjacent to the magnetic layer.

Additional features and advantages are realized through the techniquesof the present invention. Other embodiments and aspects of the inventionare described in detail herein and are considered a part of the claimedinvention. For a better understanding of the invention with theadvantages and the features, refer to the description and to thedrawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The forgoing and other features, and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings in which:

FIG. 1A illustrates a cross-sectional view of a three layer device withperpendicular magnetic anisotropy according to an embodiment.

FIG. 1B illustrates a graph of the perpendicular magnetic field and agraph of the in-plane magnetic field according to an embodiment.

FIG. 2A illustrates a cross-sectional view of a spin torque transferrandom access memory (STT-RAM) device according to an embodiment.

FIG. 2B illustrates an example of the STT-RAM device in which the freemagnetic layer is implemented with the three layer device according toan embodiment.

FIG. 2C illustrates an example of the STT-RAM device in which thereference magnetic layer is implemented with the three layer deviceaccording to an embodiment.

FIG. 2D illustrates an example of the STT-RAM device in which the freemagnetic layer and reference magnetic layer are respectively implementedwith separate three layer devices according to an embodiment.

FIG. 3 illustrates a hard disk drive (HDD) with the three layer deviceaccording to an embodiment.

FIG. 4 illustrates a method for forming a three layer structure devicewith perpendicular magnetic anisotropy according to an embodiment.

DETAILED DESCRIPTION

An embodiment discloses a device with perpendicular magnetization thatmay be utilized in various applications.

Dense spin torque MRAM requires magnetic layers with magnetizationperpendicular to the plane with large magnetic anisotropy, andcompatible with MgO to give high magnetoresistance. State of the artwork has shown that Ta|CoFeB|MgO satisfies these requirements.

However, the anisotropy may not be large enough to make devices for the20 nanometer node size and below. Also, magnetic layers withmagnetization perpendicular to the plane with large magnetic anisotropywould also be useful for hard disk drive storage media.

Magnetic anisotropy is the directional dependence of a material'smagnetic properties. In the absence of an applied magnetic field, amagnetically isotropic material has no preferential direction for itsmagnetic moment, while a magnetically anisotropic material will alignits moment with one of the easy axes (as discussed herein perpendicularmagnetic anisotropy (PMA) is aligned perpendicularly). An easy axis isan energetically favorable direction of spontaneous magnetization thatis determined by the sources of magnetic anisotropy.

Embodiments disclose structures that have high perpendicular magneticanisotropy energy density. Perpendicular magnetic anisotropy energydensity refers to the product of free layer saturation magnetizationM_(s), free layer thickness t, and perpendicular anisotropy field H_(k).

Now turning to the figures, FIG. 1 illustrates a cross-sectional view ofa three layer device 100 with perpendicular magnetic anisotropyaccording to an embodiment. The device 100 includes a magnetic layer 110containing iron (Fe), sandwiched in between a top oxide layer 105 and abottom oxide layer 115. As understood by one skilled in the art, theoxide layers contain oxygen.

In the device 100, the Fe—O bonds on both interfaces 150 and 160 toproduce very large perpendicular magnetic anisotropy (i.e., verticalmagnetization in device 100). In other words, the iron of the magneticlayer 110 bonds with the oxygen in the top oxide layer 105 at interface150 and the iron of the magnetic layer 110 bonds with the oxygen in thebottom oxide layer 115 at interface 160 to produce the largeperpendicular magnetic anisotropy for the device 100. The device 100provides a simple perpendicular material system with large perpendicularmagnetic anisotropy that can be utilized in various applications asdiscussed further herein. As compared to CoFeB layers with a singleoxide interface, the M_(s)tH_(k) of samples with double oxide interfacescan be improved by 5× or more. FIG. 1B shows one example of such astructure where the bottom oxide layer is MgO and top oxide layer isMgTiOx. In this particular sample, the M_(s)tH_(k) product is ˜1.1ergs/cm², compared to ˜0.2 erg/cm² for a typical MgO|CoFeB|Ta sample.

In FIG. 1B, a chart 170 shows the magnetic perpendicular field (i.e.,vertical) strength (in Oersteds (Oe)) on the horizontal axis and showsthe moment (M_(s)t in emu/cm²) on the vertical axis for the structure,where EMU is the electromagnetic unit. The line 172 shows the measuredmagnetic moment when a perpendicular magnetic field is applied whichtraverses from a positive magnetic field (e.g., +800 Oe) to negativemagnetic field (e.g., −800 Oe). Line 174 shows the measured magneticmoment when the perpendicular magnetic field is applied which traversefrom a negative magnetic field (e.g., −800 Oe) to positive magneticfield (e.g., +800 Oe). In chart 170, the saturation moment (when theperpendicular magnetic field is applied) is denoted by 176.

In FIG. 1B, a chart 180 shows the magnetic in-plane field (i.e.,horizontal) strength (in kilo Oersteds (kOe)) on the horizontal axis andshows the moment (M_(s)t in emu/cm²) on the vertical axis for thestructure. The line 182 shows the measured magnetic moment when thein-plane magnetic field is applied which traverses from a positivemagnetic field (e.g., +15 kOe) to negative magnetic field (e.g., −15kOe). Line 184 shows the measured magnetic moment when the in-planemagnetic field is applied which traverse from a negative magnetic field(e.g., −15 kOe) to positive magnetic field (e.g., +15 kOe). In chart180, the saturation in-plane magnetic field is denoted by 186 and thevalue is H_(k)=10 kOe.

M_(s) is the saturation magnetization of the free layer material, t isthe thickness of the free layer, and H_(k) is the perpendicularanisotropy field of the free layer. The M_(s)tH_(k) product is referredto as energy density. For a given device size, the higher theM_(s)tH_(k) product, the higher the thermal activation energy barrierwhich translates to better retention. Perpendicular magnetic anisotropyenergy density refers to the product of free layer saturationmagnetization M_(s), free layer thickness t, and perpendicularanisotropy field H_(k).

The device 100 is compatible with MgO for high magnetoresistance if oneof the oxide layers 105 and/or 115 is MgO.

The device 100 can be formed as discussed below. The bottom oxide layer115 is grown first, and then the Fe-containing magnetic layer 110 isgrown on top of the bottom oxide layer 115. Next, the top oxide layer105 is grown on top of the magnetic layer 110.

The top oxide layer 105 may include MgO, AlO_(x), HfO_(x), TiO_(x),TaO_(x), CuO_(x), VO_(x), RuO_(x), SiO_(x), WO_(x), BO_(x), CaO_(x),ScO_(x), ZnO_(x), CrO_(x), MnO_(x) and/or any other oxide, includingcombinations of oxides, mulitcomponent oxides, and multilayered oxides.Also, the bottom oxide layer 115 may include MgO, AlO_(x), HfO_(x),TiO_(x), TaO_(x), CuO_(x), VO_(x), RuO_(x), SiO_(x), WO_(x), BO_(x),CaO_(x), ScO_(x), ZnO_(x), CrO_(x), MnO_(x), and/or any other oxide,including combinations of oxides, mulitcomponent oxides, andmultilayered oxides. The “x” subscript is a variable that represents thenumber of atoms of the oxygen element (to form the oxide), which canapply to any varied number of atoms suitable for the compound of anoxide as understood by one skilled in the art.

The Fe-containing magnetic layer 110 may include Fe, CoFe, CoFeB,CoFeBTa, and/or any other Fe-containing magnetic layer, includingcombinations of magnetic materials, magnetic alloys, and multilayeredmagnetic materials, as long as the materials (of the magnetic layer 110)at the interfaces 150 and 160 with the oxides contain Fe. A particularembodiment is MgO|CoFeB|MgO, where the bottom oxide layer 115 is MgO,the magnetic layer 110 is CoFeB, and the top oxide layer 105 is MgO.

The Fe-containing magnetic layer 110 may be 10-50 angstroms (Å) thick.The top oxide layer 105 may be 2-20 angstroms thick. The bottom oxidelayer 115 may be 2-20 angstroms thick.

The device 100 may be utilized in a spin torque MRAM device (as the freelayer, and/or reference layers (or part of the reference layers)), asthe media in hard disk drives, and/or in any other application where aperpendicularly magnetized structure is needed.

There are various applications for the device 100, and a few examplesare discussed in FIGS. 2A, 2B, 2C, and 2D (generally referred to as FIG.2). FIG. 2A illustrates a cross-sectional view of a spin torque transferrandom access memory (STT-RAM) device 200 according to an embodiment.The device 100 may replace a reference magnetic layer 20, part of areference magnetic layer 20, and/or a free magnetic layer 40 in theSTT-RAM device 200. The device structure of the STT-RAM device 100includes a magnetic tunnel junction (MTJ) 70. The magnetic tunneljunction 70 has a reference magnetic layer 20, a tunnel barrier 30 onthe reference magnetic layer 20, and a free magnetic layer 40 on thetunnel barrier 30. The reference magnetic layer 20 is on a seed layer10. The seed layer 10 may be one or more different materials (dependingon the exact reference magnetic layer 20) to grow the reference magneticlayer 20. A cap layer 50 is disposed on top of the free magnetic layer40. The reference magnetic layer 20 and the free magnetic layer 40sandwich the tunnel barrier 30 in between. The tunnel barrier 30 is athin insulator (typically a few nanometers thick).

The free magnetic layer 40 is shown with double arrows to illustratethat spin torque current (or spin polarized current) via voltage source75 can flip the magnetic orientation of the free magnetic layer 40 to upor down as desired. The reference magnetic layer 20 is shown with an uparrow to illustrate a magnetic orientation in the up direction.

To write the STT-RAM device 100, the voltage source 75 applies voltagesuch that a spin torque current may flip the magnetic orientation of thefree magnetic layer 40 as desired. When the magnetic orientations of thefree magnetic layer 40 and the reference magnetic layer 20 are parallel(i.e., pointing in the same direction), the resistance of the MTJ 70 islow (e.g., representing logic 0). When the magnetic orientations of thefree magnetic layer 40 and the reference magnetic layer 20 areantiparallel (i.e., pointing in opposite directions), the resistance ofthe MTJ 70 is high (e.g., representing a logic 1).

FIG. 2B illustrates an example of the STT-RAM device 200 in which thefree magnetic layer 40 is implemented (or replaced) with the device 100according to an embodiment. The device 100 can also implement the tunnelbarrier 30 or vice versa as seen below.

In FIG. 2B, the device 200 includes the layers 10, 20, 30, 40, and 50.The free magnetic layer 40 now includes the bottom oxide layer 115, themagnetic layer 110 with iron, and the top oxide layer 105 (of device100). In this case, the bottom oxide layer 115 is disposed directly onthe reference layer 20, and the bottom oxide layer 115 acts as thetunnel barrier 30. The cap layer 50 is disposed on the top oxide layer105. As such, the device 100 with its perpendicular magnetization isutilized as the free magnetic layer 40. Operating as the free magneticlayer 40, the device 100 can have an upward pointing magnetization or adownward pointing magnetization based on applying voltage of the voltagesource 75 to generate spin current as understood by one skilled in theart.

As another example of utilizing the device 100 for its perpendicularmagnetic anisotropy, FIG. 2C illustrates an example of the STT-RAMdevice 200 in which the reference magnetic layer 20 is implemented (orreplaced, or partly replaced) with the device 100 according to anembodiment. Note that part of the device 100 may implement the tunnelbarrier 30 or vice versa.

In FIG. 2C, the device 200 includes the layers 10, 20, 30, 40, and 50.The reference magnetic layer 20 now includes the bottom oxide layer 115,the magnetic layer 110 with iron, and the top oxide layer 105 (of device100). The bottom oxide layer 115 is disposed on the seed layer 10, andthe free magnetic layer 40 is disposed on the top oxide layer 105(wherein the top oxide layer 105 acts as the tunnel barrier layer 30) ofthe device 100. Accordingly, the device 100 with its perpendicularmagnetization is utilized as the reference magnetic layer 20. Operatingas the reference magnetic layer 20, the device 100 may have a downwardpointing magnetization that provides a reference layer to the freemagnetic layer 40.

FIG. 2D illustrates an example of the STT-RAM device 200 in which boththe free magnetic layer 40 and the reference magnetic layer 20 (or partof the reference magnetic layer) are respectively implemented (orreplaced) with the devices 100 according to an embodiment. In this case,the reference layer 20 and the free layer 40 are sharing an oxide layer.When referring to the reference layer 20, the shared oxide layer isreferred to as top oxide layer 105 a (which may be the same as top oxidelayer 105). When referring to the free magnetic layer 40, the sharedoxide layer is referred to as bottom oxide layer 115 a (which may be thesame as bottom oxide layer 115).

In FIG. 2D, the reference magnetic layer 20 or part of the referencelayer 20 is formed by the bottom oxide layer 115, the magnetic layer 110a with iron, and the top oxide layer 105 a (of device 100). The bottomoxide layer 115 is disposed on the seed layer 10, and the top oxidelayer 105 a acts as the tunnel barrier 30. Accordingly, the device 100with its perpendicular magnetization is utilized as the referencemagnetic layer 20 to provide a reference layer to the free magneticlayer 40 (e.g., during reading).

Also, in FIG. 2D, the free magnetic layer 40 includes the same bottomoxide layer 115 a (acting as the tunnel barrier 30), the magnetic layer110 b with iron, and the top oxide layer 105 (of device 100). The caplayer 50 is then disposed on the top oxide layer 105. As such, aseparate device 100 with its perpendicular magnetization is alsoutilized as is the free magnetic layer 40. Note that the magnetic layers110 a and 110 b are the same material of the magnetic layer 110.

Note that although FIGS. 2A through 2D shows the free magnetic layer 40above the reference magnetic layer 20, the location of the free magneticlayer 40 and the reference magnetic layer 20 can be interchanged suchthat the free magnetic layer 40 is below the reference magnetic layer20. In this case, the free magnetic layer 40 would be located in theprevious location of the reference magnetic layer 20, and likewise thereference magnetic layer 20 would be located in the previous location ofthe free magnetic layer 40.

Another example of utilizing the perpendicular magnetic anisotropydevice 100 is discussed in FIG. 3. FIG. 3 illustrates a hard disk drive(HDD) 300 with the perpendicular magnetic anisotropy device 100(magnetic recording media) according to an embodiment. A hard disk driveis a data storage device used for storing and retrieving digitalinformation using rapidly rotating disks (platters) coated with magneticmaterial.

The HDD 300 includes a disk/platter 305. One or more of the devices 100are deposited to cover the disk/platter 305. In the sandwiched structurediscussed above, the device 100 includes the bottom oxide layer 115, theFe magnetic layer 110 adjacent to the bottom oxide layer 115, and thetop oxide layer 105 adjacent to magnetic layer 110. Note that theindividual layers 105, 110, and 115 are not repeated in FIG. 3 for thesake of conciseness but are understood to be part of the device 100.

The HDD 300 retains its data even when powered off. Data is read in arandom-access manner, which means individual blocks of data can bestored or retrieved in any order rather than just sequentially. The HDDhas one or more rigid (“hard”) rapidly rotating disks (platters) 300with magnetic heads 310 arranged on a moving actuator arm 315 to readand write data to the device 100. As shown in FIG. 3, the magnetic head310 reads and writes to the device 100 by applying a magnetic field toflip the magnetic orientation of the device 100 (e.g., upward ordownward pointing magnetic orientation). Further details of reading andwriting with a hard disk drive are not discussed but are understood byone skilled in the art.

FIG. 4 illustrates a method 400 for forming a three layer structuredevice 100 with perpendicular magnetic anisotropy according to anembodiment. Reference can be made to FIGS. 1, 2, and 3.

The bottom oxide layer 115 is deposited at block 405, and the magneticlayer 110 is deposited on top of and adjacent to the bottom oxide layer115. The magnetic layer 110 includes iron and is magnetizedperpendicularly to the longitudinal plane of the magnetic layer 110 (andthe device 100). Note that the longitudinal plane of the magnetic layer110 is the lengthwise direction (i.e., horizontal direction) from leftto right (of vice versa) in the cross-sectional views of FIGS. 1A, 2B,2C, and 2D, while the perpendicular direction is vertical (e.g., up anddown or vice versa).

The top oxide layer 105 is deposited on top of and adjacent to themagnetic layer 110 at block 415 to form the perpendicular magneticanisotropy device 100.

The bottom oxide layer 115 may be MgO. Also, the bottom oxide layerincludes at least one of MgO, AlOx, HfOx, TiOx, TaOx, CuOx, VOx, RuOx,SiOx, WOx, BOx, CaOx, ScOx, ZnOx, CrOx, MnOx, and combinations thereof.

The top oxide layer 105 may be MgO. Additionally, the top oxide layer105 includes at least one of MgO, AlOx, HfOx, TiOx, TaOx, CuOx, VOx,RuOx, SiOx, WOx, BOx, CaOx, ScOx, ZnOx, CrOx, MnOx, and combinationsthereof.

The magnetic layer 110 may be CoFeB. Further, the magnetic layerincludes at least one of CoFe, CoFeB, CoFeBTa, and combinations thereof.

With reference to FIG. 2, a free magnetic layer 40 in a spin torque MRAMdevice 200 may be formed by the bottom oxide layer 115, the Fecontaining magnetic layer 110, and the top oxide layer 105 of device100. Also, a reference magnetic layer 20 in a spin torque MRAM device200 may be formed by the bottom oxide layer 115, the Fe containingmagnetic layer 110, and the top oxide layer 105 of device 100.

With reference to FIG. 3, a disk/patter 305 in a hard disk drive 300 isformed by deposition of the bottom oxide layer 115, the magnetic layer110, and the top oxide layer 105 (to be the storage media for readingand writing).

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, element components,and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

The diagrams depicted herein are just one example. There may be manyvariations to this diagram or the steps (or operations) describedtherein without departing from the spirit of the invention. Forinstance, the steps may be performed in a differing order or steps maybe added, deleted or modified. All of these variations are considered apart of the claimed invention.

While the preferred embodiment to the invention had been described, itwill be understood that those skilled in the art, both now and in thefuture, may make various improvements and enhancements which fall withinthe scope of the claims which follow. These claims should be construedto maintain the proper protection for the invention first described.

1. A structure with perpendicular magnetic anisotropy, comprising: abottom oxide layer; a magnetic layer disposed on top of the bottom oxidelayer, wherein the magnetic layer includes iron and is magnetizedperpendicularly to a longitudinal plane of the magnetic layer; and a topoxide layer disposed on top of the magnetic layer.
 2. The structure ofclaim 1, wherein the bottom oxide layer is MgO.
 3. The structure ofclaim 1, wherein the bottom oxide layer includes at least one of MgO,AlOx, HfOx, TiOx, TaOx, CuOx, VOx, RuOx, SiOx, WOx, BOx, CaOx, ScOx,ZnOx, CrOx, MnOx, and combinations thereof.
 4. The structure of claim 1,wherein the top oxide layer is MgO.
 5. The structure of claim 1, whereinthe top oxide layer includes at least one of MgO, AlOx, HfOx, TiOx,TaOx, CuOx, VOx, RuOx, SiOx, WOx, BOx, CaOx, ScOx, ZnOx, CrOx, MnOx, andcombinations thereof.
 6. The structure of claim 1, wherein the magneticlayer is CoFeB.
 7. The structure of claim 1, wherein the magnetic layerincludes at least one of Fe, CoFe, CoFeB, CoFeBTa, and combinationsthereof.
 8. The structure of claim 1, wherein a free layer in a spintorque MRAM is formed by the bottom oxide layer, the magnetic layer, andthe top oxide layer.
 9. The structure of claim 1, wherein a referencelayer or part of the reference layer in a spin torque MRAM is formed bythe bottom oxide layer, the magnetic layer, and the top oxide layer. 10.The structure of claim 1, wherein a disk in a hard disk drive is formedby deposition of the bottom oxide layer, the magnetic layer, and the topoxide layer. 11-20. (canceled)